1. Field of the Invention
The present invention relates to a structure allowing for detection of a load applied to a vehicle seat. In particular, the invention is directed to such load detection structure for use in a vehicle seat, in which a load detection element is mounted between the seat and support leg members in a suspended way.
2. Description of Prior Art
There have been known a passenger detection system for detecting the presence and absence of a passenger or driver in a seat of vehicle in advance before actuating or stopping the associated mechanical elements to automatically control various functions and mechanisms built in the seat.
Normally, the passenger detection system employs various sensors (e.g. a pressure sensitive element) which detect the weight of a passenger on a seat and emit a signal to electronic control systems for automatic control of various mechanical elements related to the seat. Most of the sensors are of a simple structure which can only sense the presence and absence of passenger on a seat, but the recent high-tech control technology inevitably requires that the sensors should further detect whether the passenger is an adult or a child as with an air bag control system for instance.
To meet the demand, there have been proposed sensor systems for numerically detecting the weight of passenger or a corresponding load applied to the seat, determining whether the passenger is adult or child, according to a numerical data obtained, and then controlling and adjusting the associated mechanical elements to optimal conditions suited for the adult or child (e.g. controlling air bag), as disclosed from the Japanese Laid-Open Patent Publications No. 11-304579 for instance. As known form such publication, a load applied to the seat is detected by load sensor which includes one mode of sensor for directly sensing the load or another mode of sensor using a deformable material which directly receives the load and a strain gauge for detecting a degree of deformation of that deformable material, to thereby detect a precise load applied to the seat. In any case, the sensors directly receives a load applied to the seat and therefore it is required that a load detection system should be provided with a high sensitivity to precisely detect a weight of any person in a wide range including children and adults, and further the load detection system be provided with a high protection against an overload due to such an emergency accident as a collision. According to the Japanese Pub. No. 11-304579, there is provided a vertical movement restriction mechanism for restricting an excessive vertical movement of seat so as to prevent exertion of an excessive load on the load detection system and thus protect the load detection system itself against damage. Thus, this prior art is advantageous in attaining a high sensitivity to a load and a high protection against a damage from excessive vertical movement of seat.
The excessive vertical movement of seat is not only due to a traffic accident such as a collision, but also due to an instantaneous great load which is caused when a relatively heavy passenger suddenly sits on the seat, or due to extremely hard vertical vibrations or extraordinary instantaneous input of a great load which is caused during running of a vehicle on a rough road or when the vehicle falls in recesses in the road.
In general, most of known vertical movement restriction mechanism is designed to withstand the foregoing instantaneously applied great load and enough to protect the load detection system against deformation and damage. However, the conventional vertical movement restriction mechanism is formed by rigid constituent elements, which means that a great impact and contact will easily be caused among the parts in the abovementioned great load exertion cases and therefore, an objectionable noise will be generated from such keen contacts among the rigid constituent elements.
Although such objectionable noise generation is not any particular problem only in such emergency accident as a collision, it is with a high frequency that an instantaneous excessive exertion of great load on a vehicle seat will occur normally when a passenger suddenly sits on the seat. Such instantaneous excessive exertion of great load will cause a keen contact among rigid elements forming the above-described vertical movement restriction mechanism and result in generation of an objectionable noise therefrom. This objectionable noise gives a seat occupant an unpleasant feeling. Further, this kind of conventional load detection system includes such additional elements as arm members or the like in order to attain a high sensitivity to a load to be applied thereto, which means to require an increased parts in the detection structure, thus resulting in a more complicated structure. Furthermore, the conventional load detection system includes some members associated with a seat and support leg members as one of the constituent elements, and therefore, the assembly of the detection system as a whole becomes difficult, as a result of which, the assembling processes will be time-consuming and become slow.
In view of the above-stated drawbacks, it is therefore a primary purpose of the present invention to provide an improved load detection structure for a vehicle seat, which is of simplified structure without any objectionable noise generated there and designed to protect the associated main load detection element against damage when an excessive great load is applied thereto while maintaining a high sensitivity to a load normally applied from a weight of a seat occupant.
In order to achieve such purpose, in accordance with the present invention, the load detection structure is basically comprised of:
a load detection unit for detecting a load to be inputted from said seat, said load detection unit comprising:
a strain plate member of a generally oblong shape having a rigid yet elastic property which tends to recover itself into the generally oblong shape even after it is deflected, said strain plate member having a free end portion, a securing portion, a base end portion, and a deflectable area between said securing and base end portions;
a reinforcement plate means so provided on said strain plate member as to lie on said securing portion;
a sleeve means provided in said securing portion of said strain plate member
a strain gauge means attached firmly on said deflectable area of said strain plate member; and
a buffer cover means attached on and over said free end portion of said strain plate member;
said load detection unit being provided in said support leg means in a vertically movable manner, such that the base end portion thereof is pivotally connected between said pair of vertically extending lateral walls of said support leg member to allow vertical movement of said free end portion of the strain plate member within said support leg means;
a nut means fixed to said seat;
an opening means defined in said bottom wall of said support leg means;
a bolt means including a threaded portion to be threaded engaged in said nut means;
said load detection unit being connected at the securing portion thereof to said seat by inserting said bolt means through said opening means and said sleeve means and threadedly engaging the bolt means in said nut means;
a vertical movement limiting means for limiting vertical movement of said load detection unit, said vertical movement limiting means including a limited space defined therein and being fixedly provided in said support leg member in such a manner as to surround said buffer cover means associated with said load detection unit, thereby limiting said vertical movement of both said buffer cover means and free end portion within the limited space; and
a stopper means for preventing further vertical movement of both said buffer cover means and free end portion of the strain plate member in a direction exceeding said limited space of the vertical movement limiting means, said stopper means including a limited gap defined therein for limiting said further vertical movement,
with such an arrangement that, when an excessive great load is applied to said seat, the vertical movement of both said buffer cover means and free end portion unit due to said excessive great load is limited by said vertical movement limiting means, after which, the excessive vertical movement of said cover means and free end portion is prevented by said stopper means.
Preferably, the vertical movement limiting means may comprise a limiter ring member of generally rectangular shape having an upper portion defining an upper limit in the limited space and a lower portion defining a lower limit in the limited space, so that the buffer cover means of the load detection unit is brought to contact with one of the upper and lower portions of limiter ring member when said excessive great load is applied to the seat, thereby limiting the vertical movement of load detection unit.
Preferably, the sleeve means may include a rivet portion fixedly riveted to the securing portion of strain plate member, thereby defining a riveted end portion of the sleeve means thereon. In this connection, the stopper means may comprise the riveted end portion of sleeve means and a head portion formed on the bolt means at a side opposite to the headed portion, the head portion projecting outwardly through the opening means, such that the limited gap is defined between the head portion and riveted end portion, wherein both of the head portion and riveted end portion are larger in diameter than the opening means.
Other advantages and features of the present invention will become apparent from descriptions hereinafter, with reference to the annexed drawings.